Aioaws

* less verbose logging of webhooks
* uprev requirements 17
* switching signing of S3 requests to use `aws4` rather than legacy signing mode 18

* uprev dependencies 8, 9, 13
* fix multipart 14

* improve pypi classifiers 7bd32e8 a4fc3e9
* docstrings with links to AWS endpoints a4fc3e9
* add `full_message` to `SesWebhookInfo` 67f891e
* uprev `cryptography` c7b4552 75bceb7
* tweak and document AWS4 signing logic bcd585e f748371

* comprehensive tests for `S3` functionality, including tests against AWS 5
* add basic docs to README
* test on 3.9, improve CI 6

fix email headers in test responses